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#181034 - 09/19/08 09:36 PM Equipotential Bonding Grid  
George Little  Offline
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Joined: Jan 2004
Posts: 1,489
Michigan USA
Based on the '05 NEC, 680.26(C) asks us to install an Equipotential Bonding Grid under the pool and along the sides of the pool plus extend out 36" out from the inside wall of the pool under the deck. There is a TIA that says if the pool is a non-conductive type such as a polymer or a vinyl liner pool it does not have to be under the pool or along the sides of the pool. My question is: When we are talking about this non=conductive pool with no grid under the pool or along the sides of the pool are we still required to have a 36" grid under the deck or walking surface? My understanding is that the reason for the grid is the fact that people set on the edge of the pool with their feet in the water etc.

TIA 05-2

Last edited by George Little; 09/19/08 09:38 PM.

George Little

2017 / 2014 NEC & Related Books and Study Guides

#181038 - 09/19/08 10:42 PM Re: Equipotential Bonding Grid [Re: George Little]  
gfretwell  Offline


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Posts: 9,083
Estero,Fl,usa
That is the way I understand it.


Greg Fretwell

#181041 - 09/20/08 09:24 AM Re: Equipotential Bonding Grid [Re: gfretwell]  
renosteinke  Offline
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I think this is why the issues are so ... confusing:

You're tempted to think: A plastic pool is, more or less, insulated from the ground around it. Why should I have to have a grounding network if the deck is isolated in this way? It seems backwards .... and to serve no purpose.

Yet, that insulation is the very reason we want the grid. Let's look at it again.

Assume that, for some reason, either the deck or the water become energized. With a plastic liner acting as an insulator, you have just allowed a voltage difference to exist. Voltage difference = shock hazard.

Bond the two together, and the two are kept at the same potential ... no more shocks. Just as important, with a good bond, the fault is more likely to trip the breaker. In this arrange, it is JUST AS IMPORTANT that the 'water be bonded' as it is to have that grid.

While this approach doesn't solve every issue, it is hoped to lessen the risk. It appears this whole situation came about the moment we started using those plastic drop-in pool forms; before then, it appears that there was enough conductivity through the pool walls to prevent this from being an issue in most cases. The prevalence of plastic piping has probably also contributed to this 'voltage gradient' issue.

I wouldn't be at all surprised if the day comes when we look at deliberately treating the water for conductivity - making it sure it's very conductive - as well. We might even require the use of conductive pipe.

Remember .... it's not just a question of pool equipment. Indeed, I have one customer who, for religious reasons, deliberately constructed a pool without directly connected filters, pumps, or metal piping. Yet, there are still the lights in the pool room, the radio / sound system, and all manner of possible introduced electrical sources. Even though that particular room has no receptacles - there's no way to prevent someone from running a cord.


#181045 - 09/20/08 11:58 AM Re: Equipotential Bonding Grid [Re: renosteinke]  
George Little  Offline
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Joined: Jan 2004
Posts: 1,489
Michigan USA
Greg- I expected to hear from you and you didn't let me down. You and I agree that the grid would still be needed.
Reno- Thanks for the information and I think you were agreeing with Greg and I but you never said so in so many words smile


George Little

#181068 - 09/21/08 12:51 PM Re: Equipotential Bonding Grid [Re: George Little]  
gfretwell  Offline


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Posts: 9,083
Estero,Fl,usa
My personal opinion is you can't have too many bonding paths.
John is right, these "stray voltage" problems in pools and spas started when we got away from conductive pool shells, plumbing and decking materials.
For that matter the loss of a totally metallic water utility system took away the city wide equipotential grid that existed when the original electrical systems were designed.

I know in my own little world, I don't pour any concrete that is not bonded. My whole house, driveway, pool and spa is one big Ufer and everything is bonded to everything.


Greg Fretwell

#181070 - 09/21/08 01:11 PM Re: Equipotential Bonding Grid [Re: George Little]  
gfretwell  Offline


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Estero,Fl,usa
This does get back to the 2008 "bond the water" rule too.
That only requires a 2" long metal pipe nipple right now but I bet they make a better bond rule before this is over.
You can have conductive materials in fiberglass and that might be the real answer but it won't do anything for the million that are already out there.


Greg Fretwell

#181081 - 09/22/08 06:59 AM Re: Equipotential Bonding Grid [Re: George Little]  
SteveFehr  Offline
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Joined: Mar 2005
Posts: 1,207
Chesapeake, VA
If I recall, a properly chlorinated pool is already a fairly good conductor of electricity, and comparable to the conductivity of blood.
Originally Posted by George Little
My understanding is that the reason for the grid is the fact that people set on the edge of the pool with their feet in the water etc.
Or simply getting in or out of the pool from the deck, too. Lots of ways for the human body to become the circuit connecting the equipotential plane to the water.



#181096 - 09/22/08 06:05 PM Re: Equipotential Bonding Grid [Re: George Little]  
renosteinke  Offline
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Posts: 5,316
Blue Collar Country
You're right .. I was in agreement. I just wanted to 'step back' a bit, and put the issue in context - mainly for the education of others who might read this thread.


#181097 - 09/22/08 06:09 PM Re: Equipotential Bonding Grid [Re: SteveFehr]  
renosteinke  Offline
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Blue Collar Country
Steve, chlorinated water may be, might not be, etc. We need to look further.

The religious pool I described, for religious reasons, is NOT allowed to use treated water. Naturally, since the design is at least 3000 years old, they have some reason to believe that their rules have stood the test of time.

Another customer has a pool that is NOT chlorinated, at all. They treat with ozone.

Pool rules can also come into play with ornamental ponds, which may have plants and fish in them. Something to consider.


#181115 - 09/23/08 06:45 AM Re: Equipotential Bonding Grid [Re: renosteinke]  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,207
Chesapeake, VA
Absolute pure water - 0.055 µS/cm (20MOhms/cm)
Distilled water - 0.5 µS/cm (2MOhm/cm)
Mountain water - 1.0 µS/cm (1MOhm/cm)
Most drinking water sources - 500 to 800 µS/cm (1.4kOhm/cm)
Sea water - 56 mS/cm (18 Ohms/cm)
Max for potable water - 1055 µS/cm (1kOhm/cm)

Couldn't find the #s for typical pool water.


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